U.S. patent number 10,768,429 [Application Number 16/230,976] was granted by the patent office on 2020-09-08 for image display device.
This patent grant is currently assigned to JVCKENWOOD CORPORATION. The grantee listed for this patent is JVC KENWOOD Corporation. Invention is credited to Fumihiko Ito.
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United States Patent |
10,768,429 |
Ito |
September 8, 2020 |
Image display device
Abstract
A relay lens system forms an image displayed on an image display
unit as an intermediate image. A luminous flux of the image emitted
from the relay lens system reflected by a half mirror is incident
to a curved combiner, and the combiner reflects the incident
luminous flux to the half mirror to enable an observer to observe a
virtual image through the half mirror. The relay lens system forms
the intermediate image at an intermediate image forming position on
an optical axis before a light reflected by the half mirror is
incident to the curved combiner. The distance from the optical axis
of the curved combiner to a light emission surface of the relay
lens system is shorter than or equal to the distance from the
optical axis of the curved combiner to a maximum reflection
position.
Inventors: |
Ito; Fumihiko (Yokohama,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JVC KENWOOD Corporation |
Yokohama-shi, Kanagawa |
N/A |
JP |
|
|
Assignee: |
JVCKENWOOD CORPORATION
(Yokohama-Shi, Kanagawa, JP)
|
Family
ID: |
1000005042392 |
Appl.
No.: |
16/230,976 |
Filed: |
December 21, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190278085 A1 |
Sep 12, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 12, 2018 [JP] |
|
|
2018-043947 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
27/0172 (20130101); G02B 5/30 (20130101); G02B
3/08 (20130101); G02B 2027/011 (20130101); G02B
2027/0136 (20130101); G02B 2027/013 (20130101) |
Current International
Class: |
G02B
27/14 (20060101); G02B 27/01 (20060101); G02B
5/30 (20060101); G02B 3/08 (20060101) |
Field of
Search: |
;359/631 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Jones; James C.
Attorney, Agent or Firm: Procopio, Cory, Hargreaves &
Savitch LLP
Claims
What is claimed is:
1. An image display device comprising: an image display unit; a
relay lens system configured to form an image displayed on the
image display unit as an intermediate image; a
reflection/transmission unit configured to reflect a portion of an
incident light and to transmit the rest of the incident light; and
a curved mirror, to which a luminous flux of the image emitted from
the relay lens system and reflected by the reflection/transmission
unit is incident from the reflection/transmission unit, configured
to reflect the luminous flux incident thereto to the
reflection/transmission unit and to enable an observer to observe a
virtual image of the image through the reflection/transmission
unit, wherein: the relay lens system forms the intermediate image,
on an optical axis, at a position between a position where the
light is reflected by the reflection/transmission unit and a
position where the light reflected by the reflection/transmission
unit is incident to the curved mirror, and in a cross section
passing through an optical axis of the curved mirror and
perpendicular to a horizontal direction of a field of view of the
observer, a distance from the optical axis of the curved mirror to
a light emission surface of the relay lens system is shorter than
or equal to a distance from the optical axis of the curved mirror
to a maximum reflection position indicating a position where a
luminous flux emitted from an end of the image display unit is
reflected at the curved mirror.
2. The image display device according to claim 1, wherein when a
focal length of the curved mirror is f, and a width of the
intermediate image in the horizontal direction of the field of view
of the observer is x, a value of x/f is 0.58 or more and 1.19 or
less.
3. The image display device according to claim 1, wherein a
magnification of the relay lens system is set to a range of 0.4
times or more and 59.6 times or less.
4. The image display device according to claim 1, wherein the relay
lens system, the reflection/transmission unit, and the curved
mirror are coaxial optical systems sharing an optical axis with
each other.
5. The image display device according to claim 1, wherein the
curved mirror is a curved combiner which combines an incident light
from external environment and a reflected light of a light incident
from the reflection/transmission unit.
6. The image display device according to claim 1, wherein the
reflection/transmission unit includes a half mirror which transmits
a portion of a light and reflects at least a portion of the light
not transmitted.
7. The image display device according to claim 1, wherein the
reflection/transmission unit includes a polarization beam splitter
which reflects a light with a predetermined polarization plane and
transmits a light with a polarization plane perpendicular to the
predetermined polarization plane, and a 1/4 wavelength plate
arranged between the curved mirror and the polarization beam
splitter.
8. The image display device according to claim 1, wherein the relay
lens system includes a concave lens and a convex lens.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority
from Japanese patent application No. 2018-043947, filed on Mar. 12,
2018, the disclosure of which is incorporated herein in its
entirety by reference.
BACKGROUND
The present disclosure relates to an image display device.
Japanese Unexamined Patent Application Publication No. 2000-227574
discloses an image display device of a type which displays an image
of a small display device as a virtual image to a user. The image
display device of Japanese Unexamined Patent Application
Publication No. 2000-227574 includes a relay optical system for
forming the displayed image as an intermediate image and an
eyepiece optical system for forming an exit pupil to guide the
intermediate image to the user. The eyepiece optical system is
composed of a half mirror and a concave mirror. In the image
display device disclosed in Japanese Unexamined Patent Application
Publication No. 2000-227574, a display luminous flux emitted from
the relay optical system is reflected by the half mirror, is then
reflected in the opposite direction by the concave mirror, and then
passes through the half mirror and reaches the eyeball of the
user.
SUMMARY
In the image display device disclosed in Japanese Unexamined Patent
Application Publication No. 2000-227574, the displayed image of the
small display device is largely expanded on the image plane of the
intermediate image using the relay optical system, whereby a wide
field of view is realized. In this case, when the intermediate
image is formed on an optical member such as a half mirror or a
concave mirror, the observation image may deteriorate due to dust
or dirt attached to the optical member. Regarding this, Japanese
Unexamined Patent Application Publication No. 2000-227574 discloses
that the image plane of the intermediate image is formed between
the relay optical system and the eyepiece optical system. Further,
Japanese Unexamined Patent Application Publication No. 2000-227574
discloses that the image plane of the intermediate image may be
formed in the eyepiece optical system.
However, in the image display device disclosed in Japanese
Unexamined Patent Application Publication No. 2000-227574, when the
image plane of the intermediate image is formed between the relay
optical system and the eyepiece optical system, the distance
between the relay optical system and the half mirror must be long,
and thus there arises a problem that miniaturizing the device is
difficult. Further, when the image plane of the intermediate image
is formed in the eyepiece optical system, there may be a case in
which the image plane of the intermediate image is formed on the
optical path from a position where the light is reflected by the
concave mirror to a position where the light reaches the eyeball of
the user. In this case, the eyeball of the user cannot focus on the
virtual image, and thus there arises a problem that the user cannot
observe the virtual image.
The present disclosure provides an image display device
including:
an image display unit;
a relay lens system configured to form an image displayed on the
image display unit as an intermediate image;
a reflection/transmission unit configured to reflect a portion of
an incident light and to transmit the rest of the incident light;
and
a curved mirror, to which a luminous flux of the image emitted from
the relay lens system and reflected by the reflection/transmission
unit is incident from the reflection/transmission unit, configured
to reflect the luminous flux incident thereto to the
reflection/transmission unit and to enable an observer to observe a
virtual image of the image through the reflection/transmission
unit,
wherein:
the relay lens system forms the intermediate image, on an optical
axis, at a position between a position where the light is reflected
by the reflection/transmission unit and a position where the light
reflected by the reflection/transmission unit is incident to the
curved mirror, and
in a cross section passing through an optical axis of the curved
mirror and perpendicular to a horizontal direction of a field of
view of the observer, a distance from the optical axis of the
curved mirror to a light emission surface of the relay lens system
is shorter than or equal to a distance from the optical axis of the
curved mirror to a maximum reflection position indicating a
position where a luminous flux emitted from an end of the image
display unit is reflected at the curved mirror.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, advantages and features will be more
apparent from the following description of certain embodiments
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a perspective view showing an image display device
according to an embodiment of the present disclosure;
FIG. 2 is a top view showing the image display device;
FIG. 3 is a perspective view showing one of optical systems viewed
from the side;
FIG. 4 is an optical path diagram showing a cross section of the
optical system;
FIG. 5 is a top view showing the optical system viewed from the
top;
FIG. 6 is a perspective view showing an optical system
corresponding to one eye in a comparative example;
FIG. 7 is an optical path diagram showing a cross section of the
optical system in the comparative example;
FIG. 8 is a top view showing the optical system in the comparative
example viewed from the top; and
FIG. 9 is a graph showing the relationship between the width of the
intermediate image and the angle of view.
DETAILED DESCRIPTION
Hereinafter, an embodiment of the present disclosure will be
explained in detail with reference to the accompanying drawings.
FIGS. 1 and 2 show an image display device according to an
embodiment of the present disclosure. In the present embodiment,
the image display device is configured as a head mounted display
(HMD) 10 to be mounted on the head of a wearer (user). It should be
noted that, in the following explanation, the front facing
direction of the user's head may be referred to as "front", and the
up-and-down direction of the line of sight of the user who wears
the HMD 10 may be referred to as "vertical direction". Further, the
right-to-left direction of the line of sight of the user may be
referred to as "horizontal direction".
FIG. 1 is a perspective view of the HMD 10 viewed form the back of
the user's head, and FIG. 2 is a top view of the HMD 10 viewed from
the top of the user's head. The HMD 10 includes image display
elements 11L and 11R, relay lens systems 12L and 12R, half mirrors
13L and 13R, and curved combiners 14L and 14R. In the HMD 10, the
image display element 11L, the relay lens system 12L, the half
mirror 13L, and the curved combiners 14L constitute a left eye
optical system corresponding to the left eye EL of the user.
Beside, in the HMD 10, the image display element 11R, the relay
lens system 12R, the half mirror 13R, and the curved combiners 14R
constitute a right eye optical system corresponding to the right
eye ER of the user.
The above left eye optical system and the above right eye optical
system respectively have the angle of view in horizontal direction
of 82 degrees. The left eye optical system and the right eye
optical system are arranged so that their central axes are directed
outward by approximately 15 degrees with respect to the front face
of the user's head, and are combined with the other optical system.
The left eye optical system and the right eye optical system are
arranged symmetrically with respect to the united surface. The
overlapping portion of the field of view in the right-to-left
direction is 30 degrees, and this portion can be adapted to
so-called stereoscopic viewing. The total angle of view in the
horizontal direction is 82 degrees.times.2-30 degrees=134
degrees.
Note that the left eye optical system and the right eye optical
system basically have the same configuration. In the above
explanation, the suffixes "L" and "R" of the reference numeral of
each element indicate whether the optical element constitutes the
left eye optical system or the right eye optical system. In the
following explanation, when it is not necessary to particularly
distinguish the left eye optical system and the right eye optical
system, the suffixes "L" and "R" may be omitted.
FIG. 3 is a diagram showing one of the optical systems viewed from
the side. Further, FIG. 4 is a sectional view of the optical
system, a so-called optical path diagram, and FIG. 5 is a top view
showing the optical system viewed from the upper side. The image
display element 11 is a display device generating an image to be
displayed. For example, a display device such as an LCD (Liquid
Crystal Display) or an OLED (Organic Electro-Luminescence Display)
is used for the image display element 11. The image display element
11 has, for example, a size of 33 mm in the X direction (lateral
direction of the screen).times.22 mm in the Y direction
(longitudinal direction of the screen). The image display element
11 may be configured as a small projector, for example, projecting
an image to the position of the image display element 11 shown in
FIG. 3. The image display element 11 constitutes an image display
unit.
Here, in the image display element 11, a position indicating the
center in the X direction and the Y direction, namely the central
position of the screen, is set as P1. In addition, in the center in
the X direction, a position indicating one end in the Y direction
is set as P2, and a position indicating the other end is set as P3.
Further, in the center in the Y direction, a position indicating
one end in the X direction is set as P4, and a position indicating
the other end is set as P5. Luminous fluxes 51 to 55 respectively
emitted from the positions P1 to P5 of the image display element 11
travel toward the relay lens system 12 while they are
diverging.
In the HMD 10, the relay lens system 12, the half mirror 13, and
the curved combiner 14 are coaxial optical systems sharing the
optical axis with each other. The relay lens system 12 forms an
image displayed on the image display element 11 as an intermediate
image. The relay lens system 12 includes a concave lens 12a and a
convex lens 12b. The relay lens system 12 acts as a convex lens
having strong convergence power as a whole. For example, a Fresnel
lens can be used as the convex lens 12b. When a Fresnel lens is
used as the convex lens 12b, it is possible to suppress the
thickness of the lens, and thus it is advantageous for downsizing
the relay lens system 12.
It should be noted that the configuration of the relay lens system
12 is not particularly limited to those described above. The relay
lens system 12 may act as, for example, a convex lens having strong
convergence power as a whole. For example, in the relay lens system
12, a normal convex lens different from a Fresnel lens can be used
as the convex lens 12b. Alternatively, the relay lens system 12 may
have a configuration of only the convex lens 12b, or a
configuration including a diffractive lens.
The display luminous fluxes of the image including the luminous
fluxes 51 to 55, which are emitted from the image display element
11, are incident in the relay lens system 12 while they are
diverging. The display luminous fluxes refracted by the relay lens
system 12 travel toward the half mirror 13 while they are becoming
convergent luminous fluxes. At this time, the luminous fluxes 51 to
55 intersect at a position between the relay lens system 12 and the
half mirror 13, and then are incident on the half mirror 13 while
they are spreading. The half mirror 13 reflects a portion of the
incident light to the front (Y direction in FIG. 3, etc.), and
transmits the rest in the Z direction (downward direction) in FIG.
3, etc. The half mirror 13 reflects, for example, 50% of the
incident light and transmits the rest. The half mirror 13
constitutes a reflection/transmission unit.
The display luminous fluxes reflected by the half mirror 13 travel
toward the curved combiner 14. At this time, the state of the
luminous flux 51 becomes the most convergent at a position 21
between the half mirror 13 and the curved combiner 14, and an
intermediate image (aerial image) is formed at the position 21. It
should be noted that, with reference to FIG. 4, the position
(intermediate image forming position) 21 where the luminous flux 51
emitted from the central position of the image display element 11
forms the intermediate image and positions where the state of the
luminous fluxes 52 and 53 emitted from each end become the most
convergent are misaligned, which is due to the aberration in the
optical system. The intermediate image forming position 21 is an
imaging position of an intermediate image calculated using the
luminous flux 51 near the optical axis, and luminous fluxes near
the optical axis converge at this position to form an intermediate
image. On the other hand, a peripheral luminous flux does not
always converge on a plane standing at the intermediate image
forming position 21.
After the intermediate image forming position 21, the luminous flux
51 is incident on the curved combiner 14 while it is diverging.
Similarly, the peripheral luminous fluxes 52 to 55 are incident on
the curved combiner 14 while they are diverging. The curved
combiner 14 is a translucent concave mirror, and it transmits a
portion of incident luminous flux and reflects the rest. The curved
combiner 14 combines a light incident from the external environment
and the reflected light of the light incident from the half mirror
13. The luminous fluxes 51 to 55 reflected by the curved combiner
14 become substantially parallel light beams and travel to the half
mirror 13 in the opposite direction. The half mirror 13 reflects a
portion of the luminous flux incident from the curved combiner 14
and transmits the rest. The light transmitted through the half
mirror 13 travels toward the eye (pupil) E of the user and then is
incident on the pupil E. The luminous flux incident to the pupil E
is imaged on the retina by the imaging action of the eyeball and is
recognized as an image.
Here, a cross section passing through the optical axis of the
curved combiner 14 and perpendicular to horizontal direction of the
observer's field of view is considered. This cross section
corresponds to the cross section shown in FIG. 4. In the cross
section, a distance from the optical axis of the curved combiner 14
to a light emission surface of the relay lens system 12 is set as
L1. Further, in FIG. 4, a position where the luminous flux 53
emitted from the position P3 of the image display element 11 is
reflected by the curved combiner 14 is defined as a maximum
reflection position P.sub.r_max. In the HMD 10 according to the
present embodiment, when a distance from the optical axis of the
curved combiner 14 to the maximum reflection position P.sub.r_max
in the above cross section is set as L2, L1<=L2 is satisfied. In
this case, the light emission surface of the relay lens system 12
is closer to the optical axis than the maximum reflection position
P.sub.r_max, and thus the HMD 10 can be downsized especially in the
Z direction.
It should be noted that, in the above explanation, an example in
which the reflection/transmission unit is configured as the half
mirror 13 is explained, but the present disclosure is not limited
thereto. For example, the reflection/transmission unit may have a
configuration including a polarization beam splitter that reflects
lights with a predetermined polarization plane and transmits lights
with a polarization plane perpendicular to the predetermined
polarization plane, and 1/4 wavelength plate. In the configuration,
1/4 wavelength plate is arranged between the polarization beam
splitter and the curved combiner 14. When the polarization plane of
the light emitted from the image display element 11 is aligned with
the predetermined polarization, the polarization beam splitter
reflects most of the incident light to the curved combiner 14. The
light emitted to the curved combiner 14 passes through the 1/4
wavelength plate and becomes circular polarized light, is reflected
by the curved combiner 14, inversely passes through the 1/4
wavelength plate, its polarization plane is rotated by 90 degrees,
and passes through the polarization beam splitter. With such a
configuration, the luminous fluxes are effectively used for the
image observation, and the user can observe the bright image.
In addition, although an example in which a translucent concave
mirror is used for the curved combiner 14 is explained, the present
disclosure is not limited thereto. The HMD 10 according to the
present embodiment is not limited to a see-through type HMD capable
of observing the external environment, and may be a
non-transmissive type HMD. In this case, a curved mirror which
reflects almost the entire incident light may be used instead of
the curved combiner 14. When the HMD 10 is configured as the
see-through type device, the HMD 10 can be applied to applications
such as AR (Augmented Reality) and MR (Mixed Reality) in which the
display image of the image display element 11 is superimposed on
the scenery of the external environment. On the other hand, when
the HMD 10 is configured as the non-transmissive type device, the
HMD 10 can be applied to an application such as VR (Virtual
Reality).
An optical design example of the HMD 10 according to the present
embodiment is shown in below Table 1.
TABLE-US-00001 TABLE 1 4TH 6TH 8TH 10TH ORDER ORDER ORDER ORDER
CURVATURE VITREOUS CONIC ASPHERICAL ASPHERICAL ASPHERICAL
ASPHERICAL # NAME RADIUS SPACING MATERIAL COEFFICIENT COEFFICIENT
COEFFICIENT COEFFIC- IENT COEFFICIENT 1 VIRTUAL 0 -5000 IMAGE PLANE
2 PUPIL 0 150 PLANE 3 COMBINER -150 -75 SPECULAR SURFACE 4 INTERME-
0 -45 DIATE IMAGE PLANE 5 HALF 0 45 SPECULAR K A4 A6 A8 A10 MIRROR
SURFACE 6 FRESNEL 12.709 1.5 ACRYLIC -6.2808 .times. 10.sup.-1
-2.2086 .times. 10.sup.-5 -1.3617 .times. 10.sup.-7 0 0 LENS 7
-12.709 3 -6.2808 .times. 10.sup.-1 2.2086 .times. 10.sup.-5 1.3617
.times. 10.sup.-7 0 0 8 ASPHER- -22.231 3 SF57 -1.1042 .times.
10.sup. 7.4350 .times. 10.sup.-6 -1.5831 .times. 10.sup.-7 1.343
.times. 10.sup.-9 -2.2472 .times. 10.sup.-12 ICAL LENS 9 178.897
22.19 .sup. 1.4268 .times. 10.sup.2 1.7511 .times. 10.sup.-4
-8.1163 .times. 10.sup.-7 3.2333 .times. 10.sup.-9 -7.3796 .times.
10.sup.-12 10 DISPLAY 0 0 PLANE
In the above Table 1, the element number #10 "DISPLAY PLANE"
corresponds to the image display plane of the image display element
11. The element number #9 "ASPHERICAL LENS" corresponds to the
concave lens 12a of the relay lens system 12, and the element
number #6 "FRESNEL LENS" corresponds to the convex lens 12b. The
element numbers #9 and #7 correspond to spaces (air spaces) between
optical elements. The element number #5 "HALF MIRROR" corresponds
to the half mirror 13, and the element number #3 "COMBINER"
corresponds to the curved combiner 14. The element number #4
"INTERMEDIATE IMAGE PLANE" corresponds to the intermediate image
forming position 21, and the element number #2 "PUPIL PLANE"
corresponds to the pupil E of the user. The element number #1
"VIRTUAL IMAGE PLANE" corresponds to a plane where the virtual
image to be observed by the user is formed. Note that the screen
size of the image display element 11 is 33 mm.times.22 mm.
In the above Table 1, "SPACING" corresponds to thickness of the
lens or distance to next optical element. In "SPACING", positive
values indicate that the optical element exists in the right side
or the downward direction in FIG. 4 as viewed from the next optical
element. Further, negative values indicate that the optical element
exists in the left side in FIG. 4 as viewed from the next optical
element. For example, the spacing of the element number #1 "VIRTUAL
IMAGE PLANE" is -5000 mm. This means that "VIRTUAL IMAGE PLANE"
exits at a position 5000 mm away in left side of FIG. 4 as viewed
from the element number #2 "PUPIL". Besides, the spacing of the
element number #5 "HAFL MIRROR" is 45 mm. This means that "HALF
MIRROR" exists in the downward direction in FIG. 4 viewed from the
element number #6 "FRESNEL LENS".
The 4th, 6th 8th and 10th order aspherical coefficient values in
the above Table 1 can be calculated by the following formula using
the conic efficient and the curvature radius.
##EQU00001## ##EQU00001.2##
.times..times..times..times..times..times. ##EQU00001.3##
Here, as a comparative example, an HMD without a relay lens system
is considered. FIG. 6 is a diagram showing an optical system
corresponding to one eye in an HMD according to a comparative
example. FIG. 7 is a sectional view of the optical system, a
so-called optical path diagram, and FIG. 8 is a top view showing
the optical system viewed from the upper side. The HMD 100
according to the comparative example includes a display 101, a half
mirror 102, and a curved combiner 103. The display 101 corresponds
to the image display element 11 (refer to FIG. 3, etc.) of the HMD
10 according to the present embodiment, and the half mirror 102
corresponds to the half mirror 13 of the HMD 10. Further, the
curved combiner 103 corresponds to the curved combiner 14 of the
HMD 10.
In the display 101, a position indicating the center in the X
direction and the Y direction is set as P11. Further, in the center
in the X direction, a position indicating one end in the Y
direction is set as P12 and a position indicating the other end is
set as P13. Furthermore, in the center in the Y direction, a
position indicating one end in the X direction is set as P14, and a
position indicating the other end is set as P15. Luminous fluxes
emitted from the position P11 to P15 of the display 101 travel
toward the half mirror 102 while they are diverging.
The luminous fluxes emitted from the display 101 are incident on
the half mirror 102, and a portion of the incident luminous fluxes
is reflected to the curved combiner 103. The curved combiner 103
reflects a portion of the light incident from the half mirror 102.
The light reflected by the curved combiner 103 becomes
substantially parallel light beams and is incident on the half
mirror 102, and a portion of the incident light transmits the half
mirror 102 and then incident on the pupil E of the user. The
luminous flux incident to the pupil E is imaged on the retina by
the imaging action of the eyeball and is recognized as an image. It
is assumed that the size of the display 101 is 33 mm.times.22
mm.
When comparing FIG. 5 and FIG. 8, the horizontal angle of view is
81.8 degrees in the HMD 10 according to the present embodiment,
whereas the horizontal angle of view is 40.3 degrees in the HMD 100
according to the comparative example. Further, when comparing the
FIG. 4 and FIG. 7, the vertical angle of view is 60.0 degrees in
the HMD 10 according to the present embodiment, whereas the
vertical angle of view is 27.4 degrees in the HMD 100 according to
the comparative example. As can be seen from those, in the HMD 10
according to the present embodiment in which the relay lens system
12 is used, a wide angle of view can be obtained both in the
horizontal direction and the vertical direction.
Here, the relationship of the screen size, the curvature radius of
the curved combiner, and the angle of view will be explained. When
a half angle of view which is a half of the angle of view is set as
.theta., and a half of the screen size is set as an image height y,
the relationship between the half angle of view .theta. and the
image height y is calculated by the following equation.
y=f.times.tan .theta. (1) From the above equation, the angle of
view 2.theta. can be calculated by the following equation.
2.theta.=tan.sup.-1(y/f).times.2 (2)
In the above equations 1 and 2, f represents the focal length of an
imaging lens system, which is equal to 1/2 times of the radius of
the curved combiner.
For example, regarding to the horizontal direction, in the
comparative example, the image height (image width) is y=16.5 mm
and the focal length is f=45 mm, and the angle of view is
2.theta.=40.2 degrees. Further, in a product having a similar
configuration actually sold, the image height is y=7.2 mm and the
focal length is f=27.5 mm, and the angle of view is 2.theta.=29.3
degrees. With reference to the equation 2, it is understood that by
increasing the screen size and reducing the radius of the curved
combiner, it is possible to achieve a wide angle of view.
FIG. 9 shows the relationship of the image height (intermediate
image width), the angle of view, and the focal length of the curved
combiner. In a graph shown in FIG. 9, the vertical axis represents
the angle of view and the horizontal axis represents the
intermediate image width. In FIG. 9, the graph A shows the
relationship between the intermediate image width and the angle of
view when the focal length f of the curved combiner equals to 50
mm. Further, the graph B shows the relationship between the
intermediate image width and the angle of view when the focal
length f of the curved combiner equals to 75 mm, and the graph C
shows the relationship between the intermediate image width and the
angle of view when the focal length f of the curved combiner equals
to 100 mm.
Referring to FIG. 9, when the focal length of the curved combiner
is constant, it is understood that as the intermediate image width
becomes wider, the wider angle of view can be realized. Further,
when the intermediate image width is constant, it is understood
that as the focal length of the curved combiner becomes shorter, in
other words, the radius of the curved mirror becomes smaller, the
wider angle of view can be realized.
In the HMD 10 according to the present embodiment, the relay lens
system 12 generates the intermediate image enlarging the screen
size of the image display element 11. In this way, when the image
display element 11 and the display 101 of the HMD 100 according to
the comparative example have the same screen size, the wide angle
of view can be realized in the HMD 10 comparing to the HMD 100
according to the comparative example. When values of the present
embodiment are applied to the above equation 2, the intermediate
image width y is 66.0, the focal length f of the curved combiner is
75, and the angle of view 2.theta. is 82.7 degrees. That is to say,
the screen size is enlarged so as to be four times the actual
screen size of the image display element 11 in the present
embodiment.
It should be noted that the reason why the focal length f of the
curved combiner in the HMD 100 according to the comparative
embodiment is different from that of the HMD 10 according to the
present embodiment is because, for each configuration, values which
can realize the field of view as wide as possible and which adopt
realistic layouts are applied. Although there are some differences
according to the design, there are circumstances that the values
cannot be changed so much freely due to the arrangement of each
optical element. Further, the reason why the value of the angle of
view slightly differs from the above-mentioned value of the angle
of view is due to the aberration of the optical system.
Next, the limitation of the angle of view and the focal length f of
the curved combiner will be explained. The relationship between the
image height y and the focal length f is determined from the above
equation 1. Namely, it is determined by a below equation 3. y/f=tan
.theta. (3) It is assumed here that a reference angle of view which
can be called the wide angle of view is set the horizontal angle of
view of 60 degrees. That is, it is assumed that when the horizontal
angle of view is 60 degrees or more, the wide angle of view is
realized. By substituting 60 degrees for 0 in Equation 3, y/f=0.58
is obtained, and a condition for realizing a wide angle of view is
that the ratio of the image height y to the focal length f is 0.58
or more. The value of y/f is 0.37 in the HMD 100 according to the
comparative example, the value of y/f is 0.26 in the aforementioned
product, and the value of y/f is 0.88 in the HMD 10 according to
the present embodiment.
Subsequently, the position of the intermediate image is will be
explained. The position where the intermediate image is formed is a
position where luminous fluxes are most convergent, and if an
optical member is arranged at this position, influence of scratches
or dirt of the optical member easily appears in the image.
Regarding this, in Japanese Unexamined Patent Application
Publication No. 2000-227574, the image forming plane of the
intermediate image is formed between the relay optical system and
the eye-piece optical system or in the eye-piece optical system. As
another example, there is an example in which an optical member
such as a light guide member is used and the intermediate image is
formed in the light guide member. In contrast, in the present
embodiment, the intermediate image is arranged at a position
between the half mirror 13 and the curved combiner 14.
With reference to FIG. 4, etc., in order to make the intermediate
image large to widen the angle of view, it is necessary to separate
the position of the intermediate image away from the relay lens
system 12. However, when the intermediate image is formed at a
position away from the relay lens system 12 between the relay lens
system 12 and the half mirror 13, there arises a problem that the
entire optical system becomes large. For this reason, the position
of the intermediate image is preferably set behind the half mirror
13. On the other hand, when the intermediate image is formed at a
position between a position where the luminous fluxes are reflected
by the curved combiner 14 and a position where the luminous fluxes
are incident on the pupil E, the image cannot be formed on the
retina. Accordingly, in the present embodiment, the position of the
intermediate image is arranged on the optical axis between a
position where the luminous fluxes are reflected by the half mirror
13 and a position where the luminous fluxes are incident on the
curved combiner 14.
Next, the limitation of the screen size and the magnification of
the relay lens system will be explained. As already mentioned, the
condition for realizing the horizontal angle of view of 60 degrees
or more is that the ratio of y to f is 0.58 or more. When the
intermediate image width which satisfies the condition is
calculated with respect to the focal length f of various curved
combiners, which is as same as half of radius of the curved
combiner, below Table 2 is obtained. The intermediate image half
width x in the below Table 2 corresponds to y in the equation
3.
TABLE-US-00002 TABLE 2 THE RELATIONSHIP BETWEEN THE COMBINER f AND
THE INTERMEDIATE IMAGE HALF WIDTH x INTERMEDIATE IMAGE f(mm) HALF
WIDTH x(mm) 2.theta.(degrees) x/f 12.5 7.2 60 0.58 25 14.4 60 0.58
50 28.9 60 0.58 75 43.3 60 0.58 100 57.7 60 0.58
The size of the small display used for the HMD is about 0.2 to 2.0
in size. At this time, the half width X of the display in lateral
direction is about 2 mm to 20 mm. The radius of the combiner which
can be actually implemented in a combiner type HMD having a half
mirror is about 50 mm to 200 mm, and the focal length f is about
12.5 mm to 100 mm. When the configuration of the HMD is the above
values, and the magnification m of the relay lens system which
satisfies the condition of the horizontal angle of view of 60
degrees is calculated, below Table 3 is obtained.
TABLE-US-00003 TABLE 3 THE MAGNIFICATION OF RELAY LENS SYSTEM
SATISFYING THE CONDITION OF THE HORIZONTAL ANGLE OF VIEW OF 60
DEGREES x(mm) X(mm) M(times) x(mm) X(mm) m(times) x(mm) X(mm)
m(times) 7.2 2 3.6 7.2 10 0.7 7.2 20 0.4 14.4 2 7.2 14.4 10 1.4
14.4 20 0.7 28.9 2 14.4 28.9 10 2.9 28.9 20 1.4 43.3 2 21.7 43.3 10
4.3 43.3 20 2.2 57.7 2 28.9 57.7 10 5.8 57.7 20 2.9
With reference to FIG. 3, in cases where a small display of 0.2 to
2.0 in size is used for the HMD, it is understood that, to make the
horizontal angle of view 60 degrees or more, the magnification of
the relay lens system may be selected from a range of 0.4 times or
more to 28.9 times or less.
When similar calculation is applied with respect to the horizontal
angle of view of 80 degrees, below Tables 4 and 5 are obtained.
TABLE-US-00004 TABLE 4 THE RELATIONSHIP BETWEEN THE COMBINER f AND
THE INTERMEDIATE IMAGE HALF WIDTH x INTERMEDIATE IMAGE f(mm) HALF
WIDTH x(mm) 2.theta.(degrees) x/f 12.5 10.5 80 0.84 25 21.0 80 0.84
50 42.0 80 0.84 75 62.9 80 0.84 100 83.9 80 0.84
TABLE-US-00005 TABLE 5 THE MAGNIFICATION OF RELAY LENS SYSTEM
SATISFYING THE CONDITION OF THE HORIZONTAL ANGLE OF VIEW OF 80
DEGREES x(mm) X(mm) M(times) x(mm) X(mm) m(times) x(mm) X(mm)
m(times) 10.5 2 5.2 10.5 10 1.0 10.5 20 0.5 21.0 2 10.5 21.0 10 2.1
21.0 20 1.0 42.0 2 21.0 42.0 10 4.2 42.0 20 2.1 62.9 2 31.5 62.9 10
6.3 62.9 20 3.1 83.9 2 42.0 83.9 10 8.4 83.9 20 4.2
Further, when similar calculation is applied with respect to the
horizontal angle of view of 100 degrees, below Tables 6 and 7 are
obtained.
TABLE-US-00006 TABLE 6 THE RELATIONSHIP BETWEEN THE COMBINER f AND
THE INTERMEDIATE IMAGE HALF WIDTH x INTERMEDIATE IMAGE f(mm) HALF
WIDTH x(mm) 2.theta.(degrees) x/f 12.5 14.9 100 1.19 25 29.8 100
1.19 50 59.6 100 1.19 75 89.4 100 1.19 100 119.2 100 1.19
TABLE-US-00007 TABLE 7 THE MAGNIFICATION OF RELAY LENS SYSTEM
SATISFYING THE CONDITION OF THE HORIZONTAL ANGLE OF VIEW OF 100
DEGREES x(mm) X(mm) M(times) x(mm) X(mm) m(times) x(mm) X(mm)
m(times) 14.9 2 7.4 14.9 10 1.5 14.9 20 0.7 29.8 2 14.9 29.8 10 3.0
29.8 20 1.5 59.6 2 29.8 59.6 10 6.0 59.6 20 3.0 89.4 2 44.7 89.4 10
8.9 89.4 20 4.5 119.2 2 59.6 119.2 10 11.9 119.2 20 6.0
With reference to the Tables 3, 5, and 7, it is understood that, to
make the horizontal angle of view 60 degrees to 100 degrees per eye
which can be called the wide angle of view, the magnification of
the relay lens system may be set in a range of 0.4 times or more to
59.6 times or less.
It should be noted that, in fact, the horizontal angle of view per
eye of 100 degrees or more is practically excessive for the HMD.
The value of the ratio of y to f for realizing the horizontal angle
of view of 100 degrees is 1.19, and this value is the upper limit
of the ratio of y to f.
In summary, in the HMD 10 according to the present embodiment, an
image of the small image display element 11 is enlarged or reduced
by the relay lens system 12 and the curved combiner 14 so it can be
observed by the observer. In the present embodiment, the relay lens
system 12 forms the image of the image display element 11 as an
intermediate image at a position on the optical axis from the half
mirror 13 to the curved combiner 14. In the present embodiment,
since the intermediate image is formed at a position on the optical
axis between the half mirror 13 and the curved combiner 14, it is
possible to suppress the deterioration of the image due to dust or
dirt on an optical member. At this time, there may be a case where
luminous fluxes emitted from ends of the screen of the image
display element 11 are most convergent on the half mirror 13 or at
a position close to the half mirror 13. However, in many cases, the
user does not carefully observe the peripheral area of the image,
whereby it is not so problematic even if the image deteriorates a
little due to the dust or dirt of the optical member.
Further, in the present embodiment, in a cross section passing
through the optical axis of the curved combiner 14 and
perpendicular to the horizontal direction of a field of view of the
observer, the distance L1 from the optical axis to the light
emission surface of the relay lens system 12 system is shorter than
or equal to the distance L2 from the optical axis to the maximum
reflection position P.sub.r_max. By doing so, the HMD 10 can be
downsized particularly in the vertical direction.
It should be noted that although an example in which the HMD 10 has
a pair of right and left optical systems is explained, the present
disclosure is not limited thereto. The HMD 10 may be a device that
has one optical system either on the right or the left. Further, in
the above embodiment, although an example in which the image
display device is an HMD to be mounted on the user's head is
explained, the present disclosure is not limited thereto. The image
display device is not particularly limited to the HMD as long as it
is a device which allows the user to observe a virtual image.
While the present disclosure has been described in terms of an
embodiment, those skilled in the art will recognize that the
present disclosure can be practiced with various modifications
within the spirit and scope of the appended claims and the present
disclosure is not limited to the examples described above.
Further, the scope of the claims is not limited by the embodiments
described above.
Furthermore, it is noted that, Applicant's intent is to encompass
equivalents of all claim elements, even if amended later during
prosecution.
* * * * *